Smegma. It’s a word that once you have the faintest idea of its meaning, you can’t help but recoil and shriek out a reflexive “eww” into the endless void of the universe. It’s oozing, crusty, and utterly foul-smelling. Or at least that’s what many of us mistakenly assume it is.

So in order to separate fact from fiction, here’s the lowdown on smegma and why it’s not as awful as it sounds.

A Friend By Any Other Name
Strictly defined, smegma is the end result of dead skin cells and fatty oils primarily shed from certain parts of our genitalia; the inner cavity of the foreskin in men and the folds of the labia minora and clitoris in women. But its waxy, sometimes smelly, composition has lent it a much more provocative nickname: dick cheese. If ever there were two words you wouldn’t want in the same sentence, let alone next to each other, it’s those two.

But smegma is far from some godforsaken curse of humanity, at least usually. First things first, as ticking and tocking animal bodies, we excrete oil and water from our skin all the livelong day, and for good reason. The oily byproducts, known as sebum, coat our skin against microbial invaders and keep the skin waterproof. Likewise, smegma serves its own purpose. Namely, it helps lubricates our genitals during sex. Particularly in uncircumcised men, it helps ensure that the foreskin can easily slide on and off the glans, or head, of the penis without irritation (though cut fellows still produce it). And it’s not just a human thing, all mammals make and use smegma to their heart’s content.

Coming Out In the Wash
So where does the abject disgust toward smegma come from, aside from our general fear of anything related to our genitalia? Much like other begroaned bodily secretions like armpit sweat, it’s about cleanliness. When we regularly clean our genitals, smegma is transparent and unnoticeable, but when we don’t, it becomes opaque, white or yellow, and most of all, rank. The gunk comes from the build-up of dead skin cells trapped in the foreskin or vagina, while the smell comes from the bacterial breakdown of the oils. Harmless bacteria, not so harmless waste products. So in that very horrifying sense, smegma actually has plenty in common with cheese.

As to why we associate it with male genitalia, that’s likely because teenage boys and young adult men are an embarrassment to hygiene. Less insultingly, the level of smegma production shoots up throughout puberty and into adulthood but generally lowers the older we become, which makes sense considering its function in sexual intercourse. Not to worry, though, Dr. Joyce Wright, in an 1970 article about smegma in Sexology, assures us that in some men, "the penis remains well preserved and functional even into extreme old age." Joy. Boys who are reluctant or even ignorant about the need to regularly roll back and clean their foreskin as they mature might also explain smegma’s smelly reputation.

But there’s no need to bombard our junk with industrial-strength detergent to get rid of smegma. Just some nice warm water, and maybe a little soap every once in a while. If anything, constantly soaping down there will only make everything dry and irritated, which I’m sure no one wants.

Can smegma cause cancer?
In a word, no. But plenty of people have tried to figure out if it can. In the 1940s and 1950s, it became the latest scientific craze to gather smegma, sometimes from elderly men or horses, and douse mice in it. Just to see what happened. Thinking on it, that might literally be humankind’s worst scientific accomplishment. In a 2006 review of the smegma-cancer link published in the Journal of the European Academy of Dermatology and Venereology, the authors succinctly concluded that, "The evidence does not support the theory that smegma is a cause of genital cancer."

That said, aside from ensuring that you’ll never know the touch of a romantic partner, letting smegma build-up can be bad for your health. In severe cases, it can cause balanitis, or inflammation of the glans, by irritating the penis. Which, ow. This again tends to happen among the younger crowd.

Lastly, despite its name and early findings, mycobacterium smegmatis isn’t found in smegma, though it has been an invaluable source of knowledge due to its close relation to the worrisome germ that causes tuberculosis. Considering that the bacteria is actually located in soil, that only brings up the question of how early scientists found it in smegma in the first place. A question I never want answered.

As the 2006 review notes, it wasn’t just the smell that made people so dead set on finding a link between smegma and disease. It was the perception of sex as a dirty-minded hobby. In the 19th century, it was old hat to declare the very act of masturbation an abject sin, and along the way, both smegma and the foreskin were similarly demonized as unclean and degenerative to human health. That hysteria has mostly abated, but we’re still left with the idea that smegma is an unpleasant, unneeded part of our anatomy.

Nuts to that, I say! Evolutionarily speaking, we owe a great debt of gratitude (and our sex lives) to smegma. As long as we keep ourselves clean, there’s not a damn thing wrong with it. So next time you hear the word, instead of cringing in horror, you should instead mentally fist-bump the little oily secretion that could.

On second thought, that’s a really weird image. Just maybe not be so freaked out by it.

2. The Truth About Mucus

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Mucus is something everyone has, and some people wish they had a lot less of the stringy, gooey stuff. Sure, it can be gross to blow globs of snot into tissue after tissue when you have a cold or sinus infection, but mucus actually serves a very important purpose.

"Mucus is incredibly important for our bodies," explains Michael M. Johns III, MD, director of the Emory Voice Center and assistant professor of otolaryngology -- head and neck surgery at Emory University. "It is the oil in the engine. Without mucus, the engine seizes."

How much mucus is normal, and how much is too much? What does its color tell you about your health? Can you just get rid of it, or at least cut down on it, and how should you do that? Here are answers.

Mucus' Mission

Mucus-producing tissue lines the mouth, nose, sinuses, throat, lungs, and gastrointestinal tract. Mucus acts as a protective blanket over these surfaces, preventing the tissue underneath from drying out. "You have to keep them moist, otherwise they'll get dry and crack, and you'll have a chink in the armor," says Neil L. Kao, MD, associate professor of medicine at the University of South Carolina School of Medicine.

Mucus also acts as a sort of flypaper, trapping unwanted substances like bacteria and dust before they can get into the body -- particularly the sensitive airways. "You want to keep that environment, which is a sterile environment," free of gunk, says Johns. "Mucus is kind of sticky and thick. It's got viscosity to it that will trap things."

But mucus is more than just sticky goo. It also contains antibodies that help the body recognize invaders like bacteria and viruses, enzymes that kill the invaders it traps, protein to make the mucus gooey and stringy and very inhospitable, and a variety of cells, among other things.

Why Am I Making So Much Mucus?

Even when you're healthy, your body is a mucus-making machine, churning out about 1 to 1.5 liters of the stuff every day. Most of that mucus trickles down your throat and you don't even notice it.

However, there are times when you do notice your mucus -- usually not because you're producing more of it, but because its consistency has changed.

"Typically, the mucus changes character. It gets thicker," Johns says. "When it has mass effect you feel it, and when you feel it, you want to hock." Some people just naturally have thicker, stickier mucus than others.

It generally takes a bad cold, allergy, or contact with something irritating -- like a plate of nuclear-hot Buffalo wings -- to throw your body's mucus production into overdrive.

For instance, during an allergic response to an offending trigger, such as pollen or ragweed, mast cells in your body squeeze out a substance called histamine, which triggers sneezing, itching, and nasal stuffiness. The tissue of the mucus membranes starts leaking fluid, and your nose begins to run.

Drinking milk may also make some people produce more mucus. Kao says that's due to gustatory rhinitis, a reflex reaction that's triggered by eating. Gustatory rhinitis is also why your nose runs when you eat hot peppers. Milk proteins cause the same type of response in some people. But although you may feel like you have more phlegm, you're not going to worsen a cold by drinking a glass of milk, Johns says.

Why Does My Mucus Change Color?

If you've ever stopped to look at the contents of the tissue after you've blown your nose, you may have noticed that your mucus isn't always perfectly clear. It may be yellow, green, or have a reddish or brownish tinge to it. What do those colors mean?

You might have heard that yellow or green mucus is a clear sign that you have an infection, but despite that common misperception, the yellow or green hue isn't due to bacteria.

When you have a cold, your immune system sends white blood cells called neutrophils rushing to the area. These cells contain a greenish-colored enzyme, and in large numbers they can turn the mucus the same color.

But "you can have perfectly clear mucus and have a terrible ear and sinus infection," Kao says. If you do have an infection, you'll likely also have other symptoms, such as congestion, fever, and pressure in your face, overlying the sinuses, Johns says.

Multi-hued mucus also relates to concentration of the mucus. Thick, gooey mucus is often greenish, Kao says.

Mucus can also contain tinges of reddish or brownish blood, especially if your nose gets dried out or irritated from too much rubbing, blowing, or picking. Most of the blood comes from the area right inside the nostril, which is where most of the blood vessels in the nose are located. A small amount of blood in your mucus isn't anything to worry about, but if you're seeing large volumes of it, call your doctor.

How Can I Get Rid of Mucus?

People with chronic sinus problems who are constantly blowing their noses understandably want the goo gone. Over-the-counter antihistamines and decongestants are one way to do this. Decongestants cause the blood vessels in the lining of the nose to narrow, reducing blood flow to the area, so you're less congested and you produce less mucus.

Decongestants are fine for when you can't breathe due to a cold, but they're not so good for thick mucus in general. "The reason is the decongestants dry you up and they make the mucus thick, and often the opposite effect happens because you feel like you have thick mucus," Johns explains. So you take more decongestants and get into a vicious mucus-producing cycle. Decongestants also have side effects, which include dizziness, nervousness, and high blood pressure.

Antihistamines block or limit the action of histamines, those substances triggered by allergic reactions that cause the tissue in the nose to swell up and release more, thinner mucus (a runny nose). The main side effect of older antihistamines is drowsiness. They also can cause dry mouth, dizziness, and headache.

You can also thin out the mucus with guaifenesin, a type of medicine called an expectorant. Thinner mucus is easier to get out of the body. Possible side effects of guaifenesin are dizziness, headache, nausea, and vomiting.

Neti Pot Option

If you want to go a more natural route, an alternative for removing mucus is with nasal irrigation. The neti pot, a little teapot-shaped device, is one form of nasal irrigation. Others include the bulb syringe or squeeze bottle.

Every nasal irrigation method works by the same basic principle: You shoot a saline (salty water) solution up one nostril to loosen up all the mucus that's collected in your nasal cavity, which then drains out the other nostril. It's similar to cleaning gunked-up food off a dinner plate in the dishwasher, Kao says.

According to the CDC, if you are irrigating, flushing, or rinsing your sinuses, use distilled, sterile, or previously boiled water to make up the irrigation solution. It’s also important to rinse the irrigation device after each use and leave open to air dry.

Nasal irrigation is a good thing, but as the old saying goes, it is possible to have too much of a good thing. Rinsing out your sinuses washes out the bad, nasty bacteria and other critters that can cause infection. However, one study showed that when people do it too often, nasal irrigation might actually increase the risk of infection because it also washes away some of the protective substances that help prevent you from getting sick. So use your neti pot or other nasal irrigation device when you need it, but take a break from it when you feel better.

3. Scientists bust myth that our bodies have more bacteria than human cells

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It's often said that the bacteria and other microbes in our body outnumber our own cells by about ten to one. That's a myth that should be forgotten, say researchers in Israel and Canada. The ratio between resident microbes and human cells is more likely to be one-to-one, they calculate.

A 'reference man' (one who is 70 kilograms, 20–30 years old and 1.7 metres tall) contains on average about 30 trillion human cells and 39 trillion bacteria, say Ron Milo and Ron Sender at the Weizmann Institute of Science in Rehovot, Israel, and Shai Fuchs at the Hospital for Sick Children in Toronto, Canada.

Those numbers are approximate — another person might have half as many or twice as many bacteria, for example — but far from the 10:1 ratio commonly assumed.

“The numbers are similar enough that each defecation event may flip the ratio to favour human cells over bacteria,” they delicately conclude in a manuscript posted to the preprint server bioRxiv1.

The 10:1 myth persisted from a 1972 estimate by microbiologist Thomas Luckey, which was “elegantly performed, yet was probably never meant to be widely quoted decades later”, say the paper’s authors. In 2014, molecular biologist Judah Rosner at the US National Institutes of Health at Bethesda, expressed his doubts about the 10:1 claim, noting that there were very few good estimates for the numbers of human and microbial cells in the body.

Milo, Sender and Fuchs decided to re-estimate the number by reviewing a wide range of recent experimental data in the literature, including DNA analyses to calculate cell number and magnetic-resonance imaging to calculate organ volume. The vast majority of human cells are red blood cells, they note (see 'Counting human cells').

Faecal factor
A particular overestimate in Luckey’s work relates to the proportion of bacteria in our guts, Milo and colleagues say. Luckey estimated that guts contain around 1014 bacteria, by assuming that there were 1011 bacteria in a gram of faeces, and scaling that up by the one-litre volume of the alimentary canal, which stretches from the mouth to the anus.

But most bacteria reside only in the colon (which has a volume of 0.4 litres), Milo and colleagues point out — and measurements suggest that there are fewer bacteria in stool samples than Luckey thought.

Putting together these kinds of calculations, the researchers produce a ratio for microbial to human cells for the average man of 1.3:1, with a wide uncertainty. Milo declined to comment on the paper, because it is in review at a scientific journal.

“It is good that we all now have a better estimate to quote,” says Peer Bork, a bioinformatician at the European Molecular Biology Laboratory in Heidelberg, Germany, who works on the human and other complex microbiomes. “But I don’t think it will actually have any biological significance.”

4. Nausea and Vomiting

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Is Vomiting Harmful?

Usually, vomiting is harmless, but it can be a sign of a more serious illness. Some examples of serious conditions that may result in nausea or vomiting include concussions, meningitis (infection of the membrane linings of the brain), intestinal blockage, appendicitis, and brain tumors.

Another concern is dehydration. Adults have a lower risk of becoming dehydrated, because they can usually detect the symptoms of dehydration (such as increased thirst and dry lips or mouth). But young children have a greater risk of becoming dehydrated, especially if they also have diarrhea, because they often are unable to communicate symptoms of dehydration. Adults caring for sick children need to be aware of these visible signs of dehydration: dry lips and mouth, sunken eyes, and rapid breathing or pulse. In infants, also watch for decreased urination and a sunken fontanelle (soft spot on top of the baby's head).

Recurrent vomiting in pregnancy can lead to a serious condition called hyperemesis gravidarum in which the mother may develop fluid and mineral imbalances that can endanger her life or that of her unborn child.

Rarely, excessive vomiting can tear the lining of the esophagus, also known as a Mallory-Weiss tear. If the esophagus is ruptured, this is called Boerhaave's syndrome, and is a medical emergency.

When to Call the Doctor About Nausea and Vomiting

Call a doctor about nausea and vomiting:

If the nausea lasts for more than a few days or if there is a possibility of being pregnant

If home treatment is not working, dehydration is present, or a known injury has occurred (such as head injury or infection) that may be causing the vomiting

Adults should consult a doctor if vomiting occurs for more than one day, diarrhea and vomiting last more than 24 hours, or there are signs of dehydration.

Take an infant or child under six years to the doctor if vomiting lasts more than a few hours, diarrhea is present, signs of dehydration occur, there is a fever, or if the child hasn't urinated for 4-6 hours.

Take a child over age six years to the doctor if vomiting lasts one day, diarrhea combined with vomiting lasts for more than 24 hours, there are any signs of dehydration, there is a fever higher than 101 degrees, or the child hasn't urinated for six hours.

You should seek immediate medical care if any of the following situations occur with vomiting:

There is blood in the vomit (bright red or "coffee grounds" in appearance)

Severe headache or stiff neck

Lethargy, confusion, or a decreased alertness

Severe abdominal pain

Diarrhea

Rapid breathing or pulse

5. Pus - What Is Pus?

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Pus is a protein-rich fluid called liquor puris, usually whitish-yellow, yellow, or yellow brown in color. Pus consists of a buildup of dead leukocytes (white blood cells) from the body's immune system in response to infection. It accumulates at the site of inflammation. When the buildup is on or very near the surface of the skin it is called a pustule or pimple. An accumulation of pus in an enclosed tissue space is called an abscess.

Pus is a fluid that had filtered from the circulatory system into an area of inflammation caused by an infection; an exudate.

What causes a pus accumulation?
The presence of pus is the result of our body's natural immune system responding to an infection, usually caused by bacteria or fungi. When the body detects an infection, our immune system immediately reacts to get rid of it and limit the damage.

Leukocytes (white blood cells), which are produced in the marrow of bones, attack the organism that are causing the infection. Neutrophils, a type of leukocyte, have the specific task of attacking harmful fungi or bacteria.

Another type of leukocyte, called macrophages, detect the foreign bodies and release an alarm system in the form of small cell-signaling protein molecules called cytokines. Cytokines alert the neutrophils, which filter from the bloodstream into the affected area.

Experts say that the neutrophils are within the affected area about an hour after an infection starts. The rapid accumulation of neutrophils eventually leads to the presence of pus - a large quantity of dead neutrophils.

Pus after surgery
Pus is a sign of infection. This brings good and bad news:

Good news - it means that the body's immune system is fighting the infection.

Bad news - it means that there is a post-surgical complication - an infection.

If the patient has a weakened immune system, which may occur if they are being administered chemotherapy, are organ transplant recipients and taking immunosuppressant medications, are HIV positive, or have poorly controlled diabetes, the immune system may not have responded properly and there may be an infection with no pus.

People who have undergone surgery and detect the discharge of pus should tell their doctor immediately. The doctor will likely prescribe an antibiotic, ointments and recommend a special incision care program. Antibiotics help the white blood cells attack the infection, speed up the healing process, and prevent an infection complication.

Patients who have undergone surgery and are discharging pus should not slather the incision with antibiotic cream, use alcohol or peroxide. They should see their doctor or surgeon.

Why is pus yellow?
The whitish-yellow, yellow, yellow-brown, and even greenish color of pus is the result of an accumulation of dead neutrophils.

Pus can sometimes be green because some white blood cells produce a green antibacterial protein called myeloperoxidase. Pseudomonas aeruginosa, a bacterium, produces a green pigment called pyocyanin. Pus from infections caused by P. aeruginosa is particularly foul-smelling. If blood gets into the affected area the yellowish or greenish color may also have tinges of red.

Treatments for pus
The doctor will attempt to create an opening so that the pus can ooze out - doctors usually say "to evacuate".

Ubi pus, ibi evacua - this Latin adage is a medical term which means "Where pus, there evacuate" ("if there is pus, let it out"). This aphorism refers to what a doctor should do when there is pus in the body - create an opening so that it can leave the body.

Recurring otitis media (middle ear inflammation) - some children have excess fluid within the middle ear; a problem which may recur. An ear/nose and throat specialist, an otorhinolaryngologist, may recommend inserting a grommet in the eardrum to help evacuate excess fluid.

Abscesses - sometimes antibiotics are not very effective in treating an abscess; the active ingredient may find it hard to get into the abscess, or the environment may have a low pH. The doctor may insert a drainage-channel to help evacuate the pus rapidly.

Septic arthritis - an extremely painful infection in a joint which originated from another infected part of the body (in some cases only the joint is infected). The affected joint has a considerable accumulation of pus and general inflammation.

The doctor will first identify which bacterium is causing the infection and decide on a course of intravenously administered antibiotic. The antibiotics course may last several weeks.

Joint drainage - a flexible tube with a video camera at its tip, an arthroscope, is placed in the joint through a tiny incision. The doctor then inserts suction and drainage tubes around the joint to suck out the infected synovial fluid. Arthrocentesis refers to the removal of the infected fluid with a needle. The extracted fluid is examined for bacteria - the arthrocentesis is repeated every day until there is no more bacteria in the fluid.

Earwax is useful stuff. Some ancient physicians smeared it onto wounds as a soothing salve. Others thought its taste should be used as a diagnostic tool: a hint of sweetness, one doctor wrote, was a sign of impending death. Even today, doctors say it’s the most natural of soaps, carrying dead skin cells and debris out of hearing’s way.

But the near-magical properties of earwax — or cerumen, as scientists call it — don’t stop people from going to extraordinary lengths to get rid of it. No tool seems too pointy for people to want to stick into their ears.

“You name it: bobby pins, pencils, pens,” said Dr. David Jung, an otolaryngologist at Massachusetts Eye and Ear, when asked how his patients attempt earwax removal. “I’ve had some construction workers say, ‘Gently, with nails.’ I’ve seen and heard it all.”

In case you were thinking of cleaning inside your ears — gently or otherwise — a revised set of guidelines from the American Academy of Otolaryngology has some advice: Don’t. Not even with Q-tips, no matter how innocuous they look.

This recommendation is nothing new. Back in 1901, the monthly Medical Brief advised that “in the removal of impacted cerumen, as little instrumentation as possible should be indulged in. Much harm often follows the use of probes, forceps, and hooks in untrained hands.”

Few pieces of medical advice have been so consistent for so long, and by now, people know they’re not supposed to put foreign bodies in their ears — as evidenced by the sheepishness with which Jung’s patients admit to their wax-scraping tricks.

The problem is, they do it anyway. The new guidelines cite one study — titled “What health professionals at the Jos University Teaching Hospital insert in their ears”— in which over 90 percent of the participating staff at a medical center were found to clean their ear canals with objects such as Q-tips or matchsticks.

“When you put it on the inside of your ear and move it around, it feels nice, it becomes a sensual thing. You become like a drug addict, a cigarette smoker,” said Dr. Vito Forte, a professor of otolaryngology at the University of Toronto, who runs the company OtoSim, which makes ear-exam simulators.

Your ear canal is a tube closed off at one end by your eardrum. When you chew and talk, that helps move wax out towards the opening so it doesn’t impede hearing. Inserting a Q-tip or a screwdriver actually reverses that motion, pushing wax back where you don’t want it to be, sometimes creating hardened balls of wax. Then it becomes a job for an otolaryngologist, who might use a tiny suction-tip or beak-like forceps to pull it out.

The tools involved might be minuscule, but the impact isn’t: In 2012, the Medicare program paid nearly $47 million for over a million removals of earwax balls. Not all of those blockages were caused by rogue ear-cleaners — but their picking and scratching is certainly part of the problem.

Sticking things into your ears is not only ineffective — it’s dangerous. “Even though cotton swabs are fairly soft, the skin within the canal is very delicate, and easy to scratch and abrade,” said Dr. Seth Schwartz, an otolaryngologist at Virginia Mason Medical Center in Seattle and the first author of the revised guidelines. “It can be quite painful but can also lead to infection. And you could actually traumatize the eardrum.”

In that case, he said, sometimes the only option is surgery, in which the eardrum is taken out and patched up with bits of the patient’s own tissue.

The new guidelines were written expressly to be more accessible to non-scientists, in the hope of finally getting across medical advice that has been ignored for centuries.

Yet ear canal cleaning is a hard habit to kick. It may be as innate as tool use itself. Forte was once called to the Toronto Zoo to treat an orangutan that seemed to be having ear trouble — and found out that the ape was known to pick up secondhand wads of chewing gum, check them for stickiness, and then use them to extract whatever might have been buried in its ears.

If only the ape had read the latest guidelines.

7. Understanding Blisters -- the Basics

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What Are Blisters?

Most blisters happen from irritation or other damage to the skin from something outside the body, such as a shoe. Some diseases can cause blisters, fluid-filled lesions between the two top, superficial, layers of the skin.

A single blister is usually from friction or a burn, typically on the hands or feet.

Blisters all over the body may be a sign of a serious, life-threatening disease; call your doctor.

What Causes Blisters?

Blisters are caused by several things:

Friction: Blisters can happen when something rubs against skin, such as a tool handle against the hand or a new pair of shoes against the ankle. Unlike corns and calluses, which develop from prolonged rubbing, friction blisters come from brief, intense rubbing on a small area.

Burns: Flames, steam, or touching a hot surface can cause blisters, as can severe sunburn or radiation.

Cold: Extreme cold can cause blisters. For example, when a wart is frozen off, a blister will grow.

Contact with irritants or allergens: Skin may blister when it comes in contact with some chemicals, cosmetics, and many plant allergens. This is called irritant or allergic contact dermatitis.

Drug reactions: Many people develop blisters as a reaction to taking certain drugs. Before prescribing any new drugs, your doctor should ask about any drug reactions you have had in the past. If you develop a blister while on medication, call your doctor.

Autoimmune diseases: Three diseases of the immune system commonly cause blisters:

Pemphigus vulgaris, a potentially fatal skin disease, causes blisters in the mouth or skin; these painful blisters become raw and crusted after bursting.

Bullous pemphigoid causes less severe blisters that heal faster and are not life-threatening; this condition is seen mostly in elderly people.

Dermatitis herpetiformis causes small, itchy blisters; it is a chronic condition that usually starts in early adulthood. It is associated with gluten sensitivity.

Infection: Blisters are a common symptom of many infectious illnesses, including chickenpox, cold sores, shingles, and a skin infection called impetigo.

Genes: There are rare genetic diseases that cause the skin to be fragile and to blister.

8. Sweat

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You're biking up a hill, pedaling as hard as you can. You're almost there and — what's this? Your back is all wet and so is your face. Don't sweat it — it's only sweat!

Your body works best when its temperature is about 98.6ºF (37ºC). When your body gets hotter than that, your brain doesn't like it — it wants your body to stay cool and comfortable. So the part of your brain that controls temperature, called the hypothalamus (say: hi-po-THAL-uh-mus), sends a message to your body, telling it to sweat.

Then special glands in your skin called — what else? — sweat glands start making sweat. Sweat is also known as perspiration (say: pur-spuh-RAY-shun), and it is made almost completely of water, with tiny amounts of other chemicals like ammonia (say: uh-MOWN-yuh), urea (say: yoo-REE-uh), salts, and sugar. (Ammonia and urea are left over when your body breaks down protein.)

The sweat leaves your skin through tiny holes called pores. When the sweat hits the air, the air makes it evaporate (this means it turns from a liquid to a vapor). As the sweat evaporates off your skin, you cool down.

Sweat is a great cooling system, but if you're sweating a lot on a hot day or after playing hard you could be losing too much water through your skin. Then you need to put liquid back in your body by drinking plenty of water so you won't get dehydrated (say: dee-HI-drayt-ed).

Why Does Sweat Smell?
Sweat isn't just wet — it can be kind of stinky, too. But the next time you get a whiff of yourself after running around outside and want to blame your sweat glands, hold on!

Sweat by itself doesn't smell at all. It's the bacteria that live on your skin that mix with the sweat and give it a stinky smell. And when you reach puberty, special hormones affect the glands in your armpits — these glands make sweat that can really smell.

Luckily, regular washing with soap and water can usually keep stinky sweat under control. Many teens and adults also find that wearing deodorant (say: dee-OH-der-ent) or antiperspirant (say: an-tee-PUR-sper-ent) helps.

So don't worry about a little sweat — it's totally normal and everybody sweats. Sometimes too much sweating can be a sign that there is something wrong in the body, but this is rare in kids. If you notice more sweat, it's usually just a sign that it's time to start using a deodorant or antiperspirant. But if you think you have a sweat problem, talk to your parent or your doctor about it.